Polyamides are used for the production of containers of various kinds by virtue of their excellent properties, including their high strength and toughness and their high resistance to chemicals. For example, fuel oil tanks or petrol tanks for motor vehicles are produced by anionic polymerization of caprolactam. This process is particularly suitable and economical for large-volume containers.
Smaller containers, such as bottles and canisters, can be produced by extrusion blowing. This process requires polyamides of high melt viscosity to guarantee the necessary stability of the tube of melt during its extrusion. Accordingly, the size of the containers which can be produced by this process is limited by the melt viscosity or rather the molecular weight of the polyamide.
Accordingly, it is possible with an extremely high molecular weight polycaprolactam to produce even relatively large containers and tanks by extrusion blowing.
High-viscosity polyamides for extrusion are generally produced by subjecting low-viscosity standard material containing no molecular weight regulators to solid-phase post-condensation. The molecular weights of the products achieved in this way are often slightly variable and are not sufficient for the production of small or medium-size containers.